AirInsight takes a close look at the GTF, CFM LEAP

AirInsight’s Ernie Arvai has a long analysis of the Pratt & Whitney Geared Turbo Fan and CFM LEAP engine.

It is very detailed, and involves information obtained from both companies.

7 Comments on “AirInsight takes a close look at the GTF, CFM LEAP

  1. Probably a bit pedantic, but are the temperatures “C” or “F”?
    Much is said about the parts count, but two things come to mind from the analysis.
    The labour input is probably going to be a lot higher for Leap and the actual turn round time for GTF overhauls may be a lot shorter, which could be of benefit to smaller airlines with a relatively small pool of spare engines.
    The graphics were excellent although the comparitive cross section diagram shows a 4 stage LPT on the Leap but states 3 stage, same as the GTF.

  2. The engine battle is more interesting than the air frame competition. CFM has expressed confidence from the beginning that they can hold their own with the LEAP. Now it appears that may be true in a practical sense. One thing is for sure. CFM will do whatever it takes to make the LEAP at least as reliable as its crurrent offerings, including very little time off wing.

  3. It should read: Tie-Shaft Rotor in the HPC section.
    As for the LPC pressure ratio in the LEAP-X: 2.6 in the LPC and 22 in the HPC would mean that the core alone would have a prssure ratio of well above 54 (you have to consider some pressure loss between the LPC and the HPC). The 2.6 pressure ratio should be the pressure ratio of the fan+LPC. The fan should have a pressure ratio north of 1.4, so the LPC is somewhere between 1.8 and 1.9 – that should be doable with three stages.
    Furthermore, I guess the core speeds should not be much different: turbine efficiency comes (mainly) via speed, so in order to get a good core efficiency, the LEAP core should run at comparable speeds than the GTF.

    • .. the LEAP core should run at comparable speeds than the GTF ..

      What are you looking at here : rpm or circumferential speed ?

      circumferential speed / mach number should be similar.
      Diameter should be significantly smaller in the GTF.

      Fan and lpt on the same shaft force you into compromises
      between fan mach-number and turbine mach-number.

      The gearbox in the GTF “unlocks” this interdependecy.

    • The LPT turns 2 1/2 times faster on the PW1500G than on the CFM56. And the fan gear ratio is 3 to 1. I believe PW is studying a fan gear ratio of 4 to 1 for larger engines.

  4. I guess PW/RR could use the fancy materials (powder), 3D earodynamics and RTM fans used on the LEAP also on future geared fan engines?

    Lets hope the GTFs high loaded, red hot gear boxes in front of the core section hold out over longer periods, under severe conditions..

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